He doesn’t suggest that we wager everything that we are on that. Nobody does. He is cautioning against assumptions made on, literally, no data at all- and I agree with that.
That said, prepare for the worst, hope for the best.
Nice to bump into another Turtledove fan.
I know that Harry never suggested betting on that assumption - but these “scientists” are essentially doing just that by wanting to broadcast the “here we are” signal.
It is just a stupid idea. If “they” are there, somewhere in the Cosmos, then we’ll eventually come across them...hopefully, very far from Earth, and without any info about where the home planet is located. Given the age of the galaxy, I wouldn’t even want to come across aliens in 10,000 years (even if our technology keeps increasing at a geometric rate), as they could easily be a million or 100 million years ahead of us. The fact is that we just don’t know...and it is best to be cautious. Any other spacefaring race WILL be the apex predator of its home planet.